1. Field of the Invention
The present invention relates to a master clutch reengagement control for an automated mechanical transmission system of the type having a clutch actuator operated by the system controller. In particular, the present invention relates to a master clutch control for controlling the rate of reengagement of a vehicular automated mechanical transmission system master clutch upon completion of a downshift.
2. Description of the Prior Art
Change-gear mechanical transmissions (i.e., transmissions shifted by engaging and disengaging selected jaw clutches), both synchronized and nonsynchronized, are well known in the prior art. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 4,497,396; 3,221,851; 4,754,665 and 4,735,109, the disclosures of which are incorporated herein by reference.
Automatic and partially automatic mechanical transmission systems wherein the operation of mechanical transmissions is at least partially automated, usually by means of sensors providing input signals to a central control unit (usually microprocessor based) which processes the signals in accordance with predetermined logic rules to issue command output signals to actuators, are also well known in the prior art as may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,361,060; 4,648,290 and 4,595,986, the disclosures of which are incorporated herein by reference.
Controls for controlling the rate of engaging the vehicle master clutch, both for start-from-stop and for dynamic shifting, are well known in the prior art. Typically, the controls involved a rapid movement to the "touch point" or point of "incipient engagement," and then a modulated continuing engagement thereafter. Examples of such controls may be seen by reference to U.S. Pat. Nos. 4,081,065; 4,638,898; 4,646,891; 4,766,967; 5,184,301; 5,316,116 and 5,335,174, the disclosures of which are incorporated herein by reference.
Briefly, in automated mechanical transmission systems of the type having non-manually controlled clutch actuators, a downshift is accomplished by the "double clutching" technique comprising disengaging the master clutch, shifting to neutral, engaging the master clutch and accelerating the engine and transmission input shaft to synchronous for the current output shaft speed and target gear ratio (ES=IS=OS * GR.sub.T), disengaging the master clutch, engaging the target gear ratio, and then reengaging the master clutch.
The prior art clutch controls were not totally satisfactory, as downshifting during rapid deceleration (i.e., during braking) and/or coasting conditions (i.e., light throttle conditions) was not as consistently smooth as desired. By way of example, during a braking operation, the vehicle speed (i.e., output shaft speed (OS)) will change rapidly and the engine speed (ES) will often go to a higher-than-desired value due to lag time and the fact that typical diesel engines, as used in heavy-duty trucks, will respond quicker to increasing fuel than to decreasing fuel. The clutch actuator is normally relatively quickly responsive to disengage the master clutch, allowing the input shaft (IS) to coast to synchronous for completion of the shift, whereupon the input shaft speed (IS=OS * GR) will continue to decelerate. Upon reengagement of the master clutch, the slip (i.e., ES-IS) will be reduced to zero. The greater the slip upon reengagement of the master clutch, the harsher the clutch reengagement.